The mechanism by which hormones regulate adipocyte metabolism involves the plasma membrane, the adenylate cyclase system, cyclic AMP, cyclic AMP dependent protein kinase and a variety of regualtory enzymes such as hormone- sensitive lipase, phosphorylasekinase, phosphorylase, etc., which are involved in different final metabolic pathways. Lipolytic hormones, such as epinephrine, glucagon, ACTH, initiate their effects by stimulating adenylate cyclase and thereby setting off a chain of biochemical events. Although insulin counteracts the physiological processes caused by these lipolytic hormones, the mechanism by which it acts is less clearly understood. Bio- chemical, morphological (electron microscopy, freeze-etching, etc.) and cell fractionation techniques will be used to analyze structurally and functionally the integrative mechanism by which hormones regulate fat cell metabolism. They key areas on which this proposal will concentrate are: 1. To characterize hormone binding sites on adipocyte plasma membranes by both biochemical and electron histochemical approaches using for the latter ferritin conjuated hormones which are immunologically and biologically active.2. To localize adenylate cyclase by electron histochemistry and relate this to hormone binding sites. 3. To determine the role of plasma membrane ATPase in the mechanism of insulin action. 4. To study enzyme (protein kinase, phosphodiesterase) and AMP distribution and compartmentalization in adipocytes and their subcellular fractions.